If you look at the mount on the camera, an APS-C camera will have both a red dot and a white square, where you line up EF and EF-S lenses, respectively, to mount them.

APS-H and FF cameras have only the red dot, and EF-S lenses cannot be mounted (unless physically modified). There's a rubber ring at the mount on EF-S lenses to protect the camera if you try mounting them on a non-APS-C body.

I have a Canon EF 85mm f/1.8 USM, can you tell me if this can be used with a FF camera?

not only CAN you use it, you absolutely SHOULD use it with a FF camera. the 85mm f/1.8 USM is an excellent lens, great for portrait and event shooting. I like it on FF far better than I like my 50mm f/1.4 USM for some reason, it's got a little less halation and some more pop to the images at f/1.8 and f/2.

not only CAN you use it, you absolutely SHOULD use it with a FF camera. the 85mm f/1.8 USM is an excellent lens, great for portrait and event shooting. I like it on FF far better than I like my 50mm f/1.4 USM for some reason, it's got a little less halation and some more pop to the images at f/1.8 and f/2.

That is good to know. I dont use it much. I have a 2.8 70-200 that I use more. But I may be buying a FF soon and will defintatly try it out with the FF. The price on the 85mm f/1.8 UMS is pretty good too (around $400).

not only CAN you use it, you absolutely SHOULD use it with a FF camera. the 85mm f/1.8 USM is an excellent lens, great for portrait and event shooting. I like it on FF far better than I like my 50mm f/1.4 USM for some reason, it's got a little less halation and some more pop to the images at f/1.8 and f/2.

That is good to know. I dont use it much. I have a 2.8 70-200 that I use more. But I may be buying a FF soon and will defintatly try it out with the FF. The price on the 85mm f/1.8 UMS is pretty good too (around $400).

I also own and use the 70-200mm f/2.8 L IS II ... but it's just a very different lens than the 85mm f/1.8. I typically use the 85 in a more intimate or casual setting where you can get a bit closer to the action and you don't want a ginormous front element drawing attention to you. the 70-200 is basically great for everything else, it gets you great mobility, great IQ, and great image stabilization.